WHAT IS FIRE?
Fire comes from a chemical process of combustion between 3 things – oxygen, some type of fuel for example wood or petrol and heat! This combustion releases heat, light and various reactions.
For instance say we are burning wood, once the wood reaches about 150 degrees Celsius, the heat decomposes some of the cellulose material that makes up the wood. Some of the decomposed materials are released as volatile gases. We know these gases as smoke. Smoke is a compound of hydrogen, carbon and oxygen. The rest of the material forms char, which is nearly pure carbon, and ash, which is all of the unburnable minerals in the wood for example calcium and potassium.
WHAT ARE FLAMES?
At a certain point in the combustion reaction, called the ignition point, flames are produced. During combustion, the atoms in the materials being burned combine with oxygen to produce different molecules. So much heat is released during these reactions that individual atoms are superheated, and as they leave the combustion zone they bleed off excess energy in the form of light. Flames consist primarily of carbon dioxide, water vapour, oxygen and nitrogen.
The main colour in a flame changes with the temperature. For example in this picture near the logs where most burning is occurring, the fire is white. Above this is the yellow region, and then above this the colour changes to orange, which is cooler. Then above this it is then red, which is even cooler.Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke.
WHY MAKE FIRE?
- Community spirit
- To cook or heat food and water
- Make charcoal
- Communication – signaling